<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>hello world - dom</title>
</head>
<body>
  <div id="app"></div>

  <script>
    // 声明一个变量，定义字符串为 hello world
    const str = '下午还敢睡觉吗？'

    document.querySelector('#app').innerHTML = str


  </script>
</body>
</html>